Partial oxidation reaction with closed cycle quench

Abstract

The present disclosure relates to a power production system that is adapted to achieve high efficiency power production with complete carbon capture when using a solid or liquid hydrocarbon or carbonaceous fuel. More particularly, the solid or liquid fuel first is partially oxidized in a partial oxidation reactor. The resulting partially oxidized stream that comprises a fuel gas is quenched, filtered, cooled, and then directed to a combustor of a power production system as the combustion fuel. The partially oxidized stream is combined with a compressed recycle CO₂ stream and oxygen. The combustion stream is expanded across a turbine to produce power and passed through a recuperator heat exchanger. The expanded and cooled exhaust stream is scrubbed to provide the recycle CO₂ stream, which is compressed and passed through the recuperator heat exchanger and the pox heat exchanger in a manner useful to provide increased efficiency to the combined systems.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional Patent Application No. 61/597,719, filed Feb. 11, 2012, the disclosure of which is incorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

The present invention is directed to systems and methods for generation of power, such as electricity, that utilize a partial oxidation reactor to achieve high efficiency combustion of a solid fuel. Particularly, the system and method can use coal as the solid fuel.

BACKGROUND

Conventional means of power production from combustion of a fuel typically lack the ability to achieve both high efficiency power generation and carbon capture and sequestration (CCS) simultaneously. This limitation is magnified when using solid fuels in the combustion reaction because of the solid and inert nitrogen gas contents remaining in the combustion product stream. Accordingly, there is an ever growing need in the art for systems and methods for high efficiency power generation allowing for a reduction in CO₂ emission and/or improved ease of sequestration of produced

One publication in the field of high efficiency power generation with CCS, U.S. Patent Application Publication No. 2011/0179799 to Allam et al. provides one solution whereby a solid fuel such as coal, lignite, pet-coke or biomass is gasified by reaction with oxygen and optionally steam in a partial oxidation reactor operating at a sufficiently high pressure and temperature to allow substantially complete conversion of the solid fuel to a gaseous fuel comprising mainly carbon monoxide and hydrogen as the combustible components together with combustion derived impurities, such as H₂S, CS₂, COS, HCN, and NH₃. The partially oxidized net product gas is cooled, ash is separated, and it is optionally compressed to allow it to be introduced as fuel into the combustion chamber of the power generation system. The operating pressure of the partial oxidation system and the power generation system can be such that no compression of the fuel gas is required. The power generation system combustor operates with an excess of O₂ present following combustion, which ensures that the fuel and combustion derived impurities are converted from the reduced to their oxidized forms comprising predominantly SO₂ and NO. The partial oxidation reactor can be provided with transpirationally cooled walls with a high pressure recycle CO₂ stream cooling the partial oxidation product gas before ash removal at a temperature level of about 800° C. Further cooling of the partial oxidation gas to about 400° C. is necessary to ensure that all fine ash particles together with solidified volatile inorganic components are condensed and filtered to prevent solid deposition, corrosion, and blockage of down-stream equipment. The cooling of the partial oxidation gas from 800° C. to 400° C. must take place in a heat exchanger with tubes for the high pressure partial oxidation gas that are resistant to metal dusting corrosion due to the Boudouard carbon forming reaction and the high CO partial pressure in the partial oxidation gas. This is shown below in Formula (1).
CO+CO═C+CO₂  (1)
The tubes must be designed to allow periodic water washing to remove solid deposits derived from the condensation of volatile inorganic components present in solid fuels, particularly coal and lignite.

Despite the advances of the above-described publication, the systems and methods described therein still do not provide a most advantageous solution to the problems arising when using solid fuels as a power production combustion fuel. Thus, there remains a need for further systems and methods for high efficiency combustion of solid fuels with CCS.

BRIEF SUMMARY OF THE DISCLOSURE

The present disclosure provides systems and methods for high efficiency power production utilizing solid fuels and achieving simultaneous carbon capture. In particular, the disclosed systems and methods can utilize a partial oxidation (POX) reactor wherein the solid fuel is combusted to produce a POX stream comprising partial oxidation products. The POX stream can be directed to a combustor wherein the at least some of the partial oxidation products are substantially completely oxidized to produce a combustion product stream. In certain embodiments, the POX reactor can be operated at pressure that is lower than the pressure in the combustor.

In specific embodiments, the POX reactor can be can be adapted to utilize a quench cooling fluid. For example, the quench cooling fluid can be introduced to cool the POX stream from the POX reaction temperature to a quenched POX stream temperature. In exemplary embodiments, the ratio of the POX reaction temperature to the quenched POX stream temperature can be about 3.25 or greater (e.g., about 3.5:1 or about 4:1). As non-limiting examples, the POX reaction temperature can about 1300° C. or greater (e.g., about 1300° C. to about 1600° C.), and the quenched POX stream temperature can be at a temperature of about 200° C. to about 400° C. The quench cooling can be carried out by direct mixing with the POX stream in the POX reactor or a separate vessel.

In other embodiments, solids (such as solid ash particles) produced during partial oxidation of the primary POX fuel can be removed by separation from the gaseous fuel gas plus vaporized quench fluid. Alternatively the quench fluid can be present as an additional liquid phase as well as in the gas phase and act as a scrubbing fluid to remove the bulk of the ash particles. A quench temperature of about 400° C. or less can be useful to prevent metal dusting by slowing down the Boudouard reaction where solid carbon is formed from reaction of CO molecules. It further can be preferable to operate the quench system so that a single phase gaseous POX product with entrained ash particles can be passed through a cyclone and filter system to remove ash particles.

In further embodiments, the mixture of the POX stream and the quench cooling fluid vapor can be additionally cooled, such as to a temperature of about 100° C. or less to provide a cooled POX stream. Quenching and/or cooling of the POX stream preferably is carried out in a manner such that a majority of the useful heat present in the quenched POX stream gas at the POX reaction temperature is recovered. The recovered heat can be, for example, transferred to the power production system to provide low temperature heating that can maximize the efficiency of the power production system, which is further described herein. In some embodiments, part or all of the quench fluid can be separated from the cooled POX stream. The recovered quench fluid can be recycled to the POX reactor.

The disclosed systems and methods are beneficial in that existing, commercially available POX reactors can be adapted for efficient integration with a power production system. Moreover, the disclosed systems and methods can be adapted for separation of gaseous products. For example, substantially pure H₂, CO, or mixtures thereof can be separated from the cooled POX stream. The disclosed systems and methods further are beneficial in that part or all of the fuel and POX-derived impurities present in the POX stream can be oxidized in the combustor of the power production system. Thereafter, such impurities can be removed (e.g., as acids and salts), such as with a condensed water stream.

In some embodiments, the present disclosure relates to a process comprising the partial oxidation of a carbonaceous or hydrocarbon fuel by combination with oxygen in a POX reactor. The fuel can include at least sulfur compounds. The POX reaction can yield a fuel gas mixture comprising at least H₂, CO, and H₂S. In further embodiments, the POX reaction can yield a fuel gas mixture comprising at least H₂, CO, H₂S, NH₃, and HCN. The POX system can be coupled to a Power Production System (PPS) in which the fuel gas can be combusted with oxygen, and heat energy formed by the combustion can be converted to power. The methods utilizing the combined POX system and PPS can be defined by a number of characteristics in various embodiments. Exemplary embodiments are provided below.

• • All impurities derived from the carbonaceous or hydrocarbon fuel, the POX process, and the oxygen derived from the oxygen plant (e.g., an air separation unit) that are present in the POX fuel gas from the POX system following quench cooling, solid ash removal, and cooling by heat exchange with recycle high pressure CO₂ from the PPS are combusted in the PPS. Exemplary impurities can be impurities that are present in excess of H₂, CO, CH₄, CO₂, H₂O, N₂, and Ar.
  • All oxidizable impurities present in the POX fuel gas can be oxidized by combustion in the PPS.
  • Sulfur compounds, such as H₂S, COS, and CS₂, that are present in the POX fuel gas can be oxidized to SO₂, SO₃, H₂O, and CO₂. Any NH₃ and HCN present in the POX fuel gas can be oxidized to NO, NO₂, H₂O, and CO₂.
  • The POX process preferably operates at a pressure of about 2 MPa or greater.
  • The PPS can be defined by generation of power utilizing a turbine with an inlet pressure of about 10 MPA or greater.
  • The PPS can be defined by generation of power utilizing a turbine with a pressure ratio of about 12 or less (inlet to outlet).
  • The POX reaction can be carried out at an adiabatic flame temperature of about 1300° C. to about 1600° C.
  • The feed to the POX reactor can be slurried with powdered solid fuel in either water, CO₂, or a combination thereof
  • The feed to the POX reactor can be defined as comprising an entrained stream of powdered solid fuel.
  • The feed to the POX reactor can be defined as comprising a liquid such as a heated stream of bitumen.
  • The POX reactor can be adapted to include an internal heat transfer section that transfers radiant heat to a portion of a high pressure recycle stream taken from the PPS at a temperature of about 250° C. or greater and returned to the PPS at a temperature below the exit temperature of the high pressure recycle stream leaving the PPS recuperator heat exchanger.
  • The direct products of the POX reaction can be quench-cooled by direct mixing with a recycled portion of cooled quenched POX fuel gas, with a portion of liquid water condensed from the cooled quenched POX fuel gas, with CO₂ recycled from the PPS, or with a combination of these three.
  • Ash arising from the fuel used in the POX process can be removed following quench cooling of the POX products and before further cooling of the POX fuel gas.
  • The temperature achieved in quench cooling of the POX stream can be at or below a temperature of about 400° C. or at a temperature at which the velocity of the BOUDOUARD reaction is sufficiently low such that no carbon deposition or metal dusting corrosion occurs in any downstream equipment in the POX system or the PPS.
  • POX products following quench cooling and ash removal can be cooled to a temperature of about 100° C. or less by using heating high pressure recycle fluid streams taken from and returned to the PPS.
  • The PPS can be defined by the mixing of combustion products in the PPS combustor with a pressurized recycle stream and the passage of the total stream through at least one PPS turbine adapted for power generation.
  • The PPS can be defined by the operation of the turbine or turbines at a final discharge pressure of about 0.1 MPa or greater or, in other embodiments, about 1 MPa or greater.
  • The PPS can be defined by the use of one or more recuperative heat exchangers that heat the previously compressed high pressure recycle stream against at least the total turbine exhaust stream or streams.
  • The PPS can be defined by the conversion of the SO₂ and SO₃ to H₂SO₄ by reaction with O₂, liquid H₂O, NO₂, and NO.
  • The PPS can be defined by the conversion of NO, NO₂, and liquid H₂O to HNO₃.
  • The PPS acid conversions can be carried out at an operating temperature corresponding to the point at which water condenses, down to a temperature at which the water and acids are separated from the cooled turbine exhaust gas at the cold end of the recuperative heat exchanger.
  • Acids plus soluble inorganic components formed by reaction with the acids and optionally diluted with condensed water from the PPS combustor can be removed for further treatment.
  • A high pressure CO₂ recycle fluid stream or streams can be used for cooling the quenched POX product gas following ash removal.
  • The high pressure CO₂ recycle fluid stream can optionally comprise more than one fluid stream taken from the PPS at more than one temperature level.
  • More than one high pressure CO₂ recycle fluid stream can be returned to the PPS at more than one temperature level.
  • One fluid stream can be taken from the PPS and returned to the PPS as more than one stream at more than one temperature level.
  • More than one fluid stream can be taken from the PPS and returned to the PPS as a single heated stream.
  • The cooled net POX fuel gas product, following cooling and separation of POX quench recycle fluid, can be compressed from the pressure at which it exits the POX system to a pressure substantially the same as the inlet pressure of the PPS combustor.
  • A fluid stream taken from the PPS for use in cooling a quenched POX product gas can be part of the pressurized recycle stream from the PPS.
  • The oxygen used in the POX system can have a purity greater than 90% molar, preferably greater than 95% molar.
  • The partially oxidized gas can be quenched with water producing a gas mixture containing at least H₂, CO, CO₂, one or more sulfur compounds (e.g., H₂S), and H₂O.
  • Cooling of the quenched POX fuel gas can be carried out with two streams of pressurized recycle gas from the PPS; the inlet temperature of the first recycle stream entering the POX heat exchanger can be at the discharge temperature of the PPS recycle CO₂ compressor; and the inlet temperature of the second recycle CO₂ stream entering the POX heat exchanger can be within 20° C. of the water dew-point in the PPS turbine exhaust stream.
  • The POX stream comprising fuel gas can be quenched with water to produce a POX gas saturated with water vapor having excess liquid water present; and the two inlet streams of pressurized recycle gas from the PPS can leave the POX heat exchanger as a single stream at a temperature within 20° C. of the POX gas dew-point temperature.
  • The POX stream can be quenched with water to produce a quenched POX stream that is above its dew-point temperature and below 400° C.; the two inlet streams entering the POX heat exchanger can be heated and combined at the temperature point corresponding to the second inlet stream temperature; a first exit heated fluid stream can be removed at a temperature within 20° C. of the POX stream dew-point temperature, and the remaining stream can be further heated and leave the POX heat exchanger at a temperature of about 380° C. to 399° C.
  • A portion of the POX fuel gas following quench cooling can be removed and passed through a catalytic shift reactor to convert CO and H₂O to H₂ and CO₂.
  • The exit gas from the shift reactor can be cooled in the quenched POX heat exchanger against recycle gas taken from and returned to the PPS.
  • The shifted gas can be mixed with a portion of the un-shifted gas and further processed to separate water, CO₂, sulfur compounds, mercury, and other volatile inorganic components, leaving a mixture comprising H₂ and CO in a ratio from 0.8 to 1 to 2.5 to 1.
  • The shifted gas alone can be further processed to produce a pure H₂ stream of greater than 99% molar.
  • The content of sulfur compounds, NH₃, HCN, and water in the H₂ or H₂ and CO streams each can be less than 1 ppm molar.
  • The separation device can be defined as a multi-bed pressure swing adsorption (PSA) system.
  • The low pressure waste gas from the PSA comprising the adsorbed products from the PSA system can be compressed to the pressure required by the PPS combustor and mixed into the total POX fuel gas flow to the PPS combustor.
  • The oxygen used for the POX of the primary fuel can be heated in the POX heat exchanger to a temperature of up to 350° C.
  • The oxygen used in the PPS combustor can be heated in the POX heat exchanger to a temperature of up to 350° C.

In some embodiments the present disclosure can relate to a process for the production of power using a combination of a POX system and a PPS, and the process can comprise the following steps:

combining a solid or liquid fuel and oxygen in a POX reactor under conditions sufficient to partially oxidize the fuel and form a POX stream comprising a fuel gas;

quenching the POX stream through combination with a quenching fluid under conditions sufficient to form a quenched POX stream at a temperature of about 400° C. or less and to solidify at least a portion of any molten solids present in the POX stream;

treating the quenched POX stream so as to remove at least a portion of any solids present therein;

directing the quenched POX stream to a POX heat exchanger and withdrawing a quantity of heat from the quenched POX stream by cooling the quenched POX stream to a temperature of about 100° C. or less against a cooling stream and form a POX fuel gas stream;

passing the POX fuel gas stream through a separator vessel and separating at least a portion of any water present in the POX fuel gas stream;

compressing the POX fuel gas stream to a pressure of about 12 MPa or greater;

combusting the POX fuel gas in a PPS combustor to form a combustion product stream (optionally with a portion of excess oxygen) at a pressure of at least about 10 MPa and a temperature of at least about 800° C.; and

expanding the combustion product stream across a PPS turbine to generate power and form an expanded PPS combustion product stream.

In specific embodiments, the process for the production of power can be further defined by a variety of characteristics that may be independently applied to a process as noted above. For example, the solid or liquid fuel can be a carbonaceous fuel. The fuel combined in the POX reactor can be an entrained stream of a powdered, solid fuel. The carbonaceous fuel specifically can be coal. The coal can be slurried with water or CO₂. The quenched POX stream can comprise ash, slag, or a combination thereof, and the step of removing solids can comprise passing the quenched POX stream through a water scrubber unit. The step of removing solids can comprise filtering the quenched POX stream so as to reduce dust load to about 4 mg or less per cubic meter of fuel gas in the quenched POX stream. The POX reactor can be operated at a POX temperature, and a ratio of the POX temperature to the temperature of the quenched POX stream can be about 2:1 or greater. The POX temperature can be about 1300° C. to about 1600° C. The POX reactor can be operated at a pressure of about 2 MPa or greater. Quenching can comprise mixing the POX stream with: a recycled portion of the cooled POX fuel gas stream exiting the heat exchanger; a portion of the water separated from the cooled POX fuel gas stream; CO₂ recycled from the PPS, water, or a combination thereof. The cooling stream in the heat exchanger can comprise a high pressure recycle fluid stream withdrawn from and returned to the PPS. The high pressure recycle fluid stream can be a recycle CO₂ fluid stream. The recycle CO₂ fluid stream can comprise CO₂ formed in the combusting of the POX fuel gas in the PPS combustor. The POX reactor can include an internal heat transfer component. The internal heat transfer component can be adapted to transfer radiant heat to a portion of a high pressure recycle stream taken from a component of the PPS at a temperature of about 250° C. or greater. The internal heat transfer component can be adapted to return the high pressure recycle stream to a component of the PPS. The PPS turbine can have an inlet pressure of about 10 MPa or greater. The PPS turbine can have an outlet pressure that is defined as a ratio of the turbine inlet to the turbine outlet. In an example embodiment, the ratio can be about 10 or less.

In further embodiments, the process for the production of power using a combination of a POX system and a PPS also can comprise:

passing the expanded PPS combustion product stream through a PPS recuperator heat exchanger and thereby withdrawing heat from the PPS combustion product stream and forming a cooled PPS combustion product stream;

optionally passing the cooled PPS combustion product stream through a water cooler;

treating the cooled PPS combustion product stream in a PPS scrubber separating at least one or H₂SO₄, HNO₃, or water-dissolved Hg salts and forming a recycle CO₂ stream; and

pressurizing the recycle CO₂ stream in a PPS compressor and forming a compressed recycle CO₂ stream.

In specific embodiments, the separating step can comprise separating conversion products H₂SO₄ and HNO₃ formed by reaction of SO₂, SO₃, NO, NO₂, H₂O, and O₂ plus condensed water and dissolved Hg salts. Passing the expanded PPS combustion product stream through the PPS recuperator heat exchanger can cool the PPS combustion product stream to a temperature below the water dew point. The fuel gas in the POX fuel gas stream entering the PPS combustor can comprise at least one fuel gas component selected from H₂, CO, and CH₄. The POX fuel gas stream entering the PPS combustor can comprise one or more impurities separate from the fuel gas and derived from the solid or liquid fuel, the partial oxidation thereof, and the oxygen. The one or more impurities can comprise at least one of a sulfur compound, NH₃, and HCN. The one or more impurities expressly can exclude N₂ and argon. Substantially all of the impurities can still be present in the POX fuel gas stream and can be combusted in the PPS combustor. All oxidizable impurities present in the POX fuel gas stream can be oxidized by the combustion in the PPS combustor. The combustion product stream from the PPS combustor can comprise a mixture of combustion products and at least a portion of the compressed recycle CO₂ stream. The withdrawn heat from the PPS combustion product stream can heat at least a portion of the compressed recycle CO₂ stream. The POX stream can be quenched with water. The water quenched POX stream can comprise at least H₂, CO, CO₂, H₂S, and H₂O. The cooling stream in the POX heat exchanger can comprise two streams of the compressed recycle CO₂. An inlet temperature of the first compressed recycle CO₂ stream entering the POX heat exchanger can be substantially the same as a temperature of the compressed recycle CO₂ stream discharged from the PPS compressor. An inlet temperature of the second compressed recycle CO₂ stream entering the POX heat exchanger can be within 20° C. of the water dew-point in the expanded PPS combustion product stream. The water quenched POX stream can be saturated with water vapor so as to comprise excess liquid water. The two compressed recycle CO₂ streams can combine in the POX heat exchanger to form a single stream. The single compressed recycle CO₂ stream exiting the POX heat exchanger can be at a temperature that is within about 20° C. of the POX fuel gas dew-point temperature. The water quenched POX stream can have a temperature that is above its dew-point temperature and below about 400° C. The two compressed recycle CO₂ streams can be heated, and the point at which the two compressed recycle CO₂ streams combine to form the single stream can be at a temperature that substantially corresponds to the inlet temperature of the second compressed recycle CO₂ stream. The single stream can be split into the following: a first exiting heated and compressed recycle CO₂ stream that exits the POX heat exchanger at a temperature that is within about 20° C. of the POX stream dew-point temperature; and a second exiting heated and compressed recycle CO₂ stream that exits the POX heat exchanger at a temperature of about 380° C. to about 399° C.

In additional embodiments, a portion of the quenched POX stream can be directed through a POX catalytic shift reactor. The POX catalytic shift reactor can be adapted to convert a mixture of CO and H₂O into a shift reactor exit gas comprising a mixture of H₂ and CO₂. The shift reactor exit gas can be cooled in the POX heat exchanger against a recycle gas taken from and returned to the PPS. The shift reactor exit gas can be mixed with a portion of the quenched POX stream and can be further processed to separate water, CO₂, sulfur compounds, Hg, and volatile inorganic compounds so as to form a mixture comprising H₂ and CO in a ratio of about 0.8:1 to about 2.5:1. The shift reactor exit gas can be further processed to form a pure H₂ stream with a purity of 99% or greater molar. The POX stream processor can be a multi-bed pressure swing adsorption (PSA) system. A low pressure waste gas from the PSA system comprising adsorbed products from the PSA system can be compressed to a PPS combustor pressure and mixed into a total fuel gas flow entering the PPS combustor. The oxygen used in the POX reactor can be heated in the POX heat exchanger to a temperature of up to about 350° C. The oxygen used in the PPS combustor can be heated in the POX heat exchanger to a temperature of about 350° C.

In other embodiments, the present disclosure can provide a combined POX system and PPS, and the combined system can be useful for producing power, such as electricity, from a starting fuel that is non-gaseous. In some embodiments, a POX system and PPS can comprise the following elements:

a POX reactor adapted to partially oxidize a liquid or solid fuel in the presence of oxygen to form a POX stream comprising a fuel gas;

one or more components adapted to contact the POX stream with a quenching fluid;

an optional POX scrubber adapted to separate any solids present in the quenched POX stream from the POX fuel gas;

a POX heat exchanger adapted to withdraw heat from the POX fuel gas against a portion of a compressed recycle CO₂ stream and output a cooled POX fuel gas;

an optional separator adapted to separate any liquid water from the POX fuel gas;

a compressor adapted to compress the cooled POX fuel gas to a pressure of about 12 MPa or greater;

a PPS combustor adapted to combust the POX fuel gas in the presence of oxygen and a portion of the compressed recycle CO₂ stream and form a PPS combustion product stream at a pressure of about 12 MPa or greater;

a turbine adapted to expand the PPS combustion product stream and generate power in a connected generator;

a recuperator heat exchanger adapted to withdraw heat from the expanded PPS combustion product stream and add the heat to the compressed recycle CO₂ stream;

a PPS scrubbing tower adapted to separate any oxidized impurities from the expanded PPS combustion product stream and output a recycle CO₂ stream;

a PPS compressor adapted to compress the recycle CO₂ stream to a pressure of about 12 MPa or greater and form the compressed recycle CO₂ stream;

flow components adapted to direct a portion of the compressed recycle CO₂ stream to the POX heat exchanger;

flow components adapted to direct a portion of the compressed recycle CO₂ stream to the PPS recuperator heat exchanger; and

flow components adapted to direct the compressed recycle CO₂ stream from the POX heat exchanger to the PPS recuperator heat exchanger.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which is not necessarily drawn to scale, and wherein:

FIG. 1 is flow sheet illustrating an example embodiment of a combined POX system and PPS according to the present disclosure wherein the PPS generates power using a fuel gas derived from the partial oxidation of a liquid or solid hydrocarbon or carbonaceous fuel in the POX system;

FIG. 2 is a flow sheet illustrating a portion of the combined system from FIG. 1, wherein the illustrated portion particularly shows elements of the combined system useful for production of export H₂ or H₂+CO mixtures;

FIG. 3 is a plot of temperature versus heat transferred in a fuel gas heat exchanger for a system according to an example embodiment of the present disclosure using a CO₂ coal slurry with a water quenched POX reaction operating with excess water so that the quenched POX fuel gas is at the water dew-point temperature;

FIG. 4 is a plot of temperature versus heat transferred in a POX heat exchanger for a system according to an example embodiment of the present disclosure using a CO₂ coal slurry with a water quenched POX reaction operating at a quench temperature of 400° C.;

FIG. 5 shows the mass and heat balance from an ASPEN simulation of a power system combining a POX system and a PPS according to an example embodiment of the present disclosure, wherein the simulation included the use of a coal/CO₂ slurry in the POX reactor and utilization of water as a quenching fluid; and

FIG. 6 shows the mass and heat balance from an ASPEN simulation of a power system combining a POX system and a PPS according to an example embodiment of the present disclosure, wherein the simulation included the use of a coal/CO₂ slurry in the POX reactor and utilization of CO₂ as a quenching fluid.

DETAILED DESCRIPTION OF THE DISCLOSURE

The invention now will be described more fully hereinafter through reference to various embodiments. These embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. As used in the specification, and in the appended claims, the singular forms “a”, “an”, “the”, include plural referents unless the context clearly dictates otherwise.

The systems and methods of the present disclosure are adapted for achieving partial oxidation (POX) of a carbonaceous fuel, particularly a solid fuel and/or a liquid fuel. Non-limiting examples of fuels that can be used according to the present disclosure include coal, lignite, petroleum coke, bitumen, biomass, algae, wood, graded combustible solid waste refuse, asphalt, used tires, crude oil, other ash containing liquid fuels, and the like.

In various embodiments, the systems and methods of the disclosure are adapted to partially oxidize the fuel using oxygen, preferably substantially pure O₂, so as to produce a stream that is useful as a fuel gas. The partial oxidation can be carried out in a POX reactor. In particular embodiments, an air separation unit or other oxygen plant can be utilized in the systems and methods of the present disclosure. Oxygen from the plant can be directed to the POX reactor. In some embodiments, the oxygen can be first passed through a heat exchanger to increase the temperature of the oxygen entering the POX reactor. Nitrogen from the air separation plant also can be incorporated into the systems and methods. For example, dry N₂ can be passed through a crusher that is particularizing solid fuels and thus partially dry the particulate fuel. The particulate fuel can be further crushed in a second crusher to a particle size preferably of about 500 microns or less, about 250 microns or less, or about 100 microns or less. The small particle fuel can be directed to a mixer to be formed into a slurry with a slurrying medium. The slurry medium can comprise CO₂, which preferably has a pressure of about of 3.5 MPa or greater, about 5 MPa or greater, or about 8.5 MPa or greater. The CO₂ in the CO₂ slurry medium preferably can be at a temperature of about 5° C. to about 40° C., about 10° C. to about 30° C., or about 12° C. to about 25° C. The CO₂ in the CO₂ slurry medium can have a density of about 500 kg/m³ to about 1000 kg/m³, about 600 kg/m³ to about 900 kg/m³, or about 700 kg/m³ to about 800 kg/m³. The slurry medium can alternately comprise water or a combination of CO₂ and water. A solid fuel slurry used in the POX reactor can comprise about 25% to about 75%, about 30% to about 70%, or about 40% to about 60% by weight solid fuel. The particulate fuel slurry is then combined in the POX reactor with the oxygen, which preferably comprises about 90% molar or greater, about 95% molar or greater, of about 97% molar or greater oxygen. The POX reactor preferably operates at a pressure of about 4.5 to about 8.5 MPa and a temperature of about 1450° C.; however, the temperature and pressure can be in any combinations of temperature and pressure ranges as otherwise disclosed herein in relation to the nature of the POX stream exiting the POX reactor.

Partial oxidation of the carbonaceous fuel in the POX reactor forms a POX stream, which can be defined in terms of the components thereof. In particular, the POX stream can comprise a fuel gas and one or more impurities (oxidizable impurities and non-oxidizable). The fuel gas can comprise hydrogen, carbon monoxide, or a combination thereof. Exemplary impurities derived from the original POX fuel (solid or liquid hydrocarbons or carbonaceous material) or the partial oxidation reactions include, for example, H₂S, COS, CS₂, HCN, NH₃, and Hg. The stream arises from the POX reactor wherein the POX stream produced therefrom can be quenched with a cooling fluid. This can result in the partial vaporization of the cooling fluid to produce a fuel gas comprising vaporized cooling fluid mixed with fuel gas. Excess quench cooling fluid can be used giving a mixture of liquid cooling fluid and vapor fuel gas plus vaporized cooling fluid as a product from the POX reactor. The cooled POX stream can undergo separation so that solids (e.g., solid ash particles) can be removed. The solids particularly can be removed in a mixture with the liquid cooling fluid that is separated from the fuel gas mixture. Any remaining fine ash particles can be removed by a downstream cooling fluid wash column followed by a candle filter or the like. Alternatively, the quench can result in a gaseous phase with entrained ash particles that are removed in a combination of cyclones and filters. The cooled POX stream thereafter can be cooled in a heat exchanger to recover at least a portion of the useful heat that was present in the POX stream prior to quench cooling. In particular, the bulk of the vaporized cooling fluid mixed with the fuel gas can be condensed, and the heat can be transferred primarily to a high pressure recycle stream to reduce the temperature difference at the hot end of a recuperative heat exchanger in the power production system. This can be particularly beneficial to increase the overall efficiency of the power production system alone or in combination with the POX system. The POX stream (i.e., the fuel gas stream) can be produced at a pressure that is less than or equal to the pressure required for further combustion of the fuel gas in the combustor for power production. For example, a combustor and associated power production cycle that can be combined with the systems and methods of the present disclosure is described in U.S. Patent Application Publication No. 2011/0179799, the disclosure of which is incorporated herein by reference in its entirety. Such combustor and associated power production cycle may be referenced herein as the “NET Power System.” The process of the NET Power System achieves power generation using predominantly CO₂ as a working fluid. In particular, the process uses a high pressure/low pressure ratio turbine that expands a mixture of a high pressure recycle CO₂ stream and combustion products arising from combustion of the fuel. Pure oxygen can be used as the oxidant in the combustion process. The hot turbine exhaust is used to partially preheat the high pressure recycle CO₂ stream. The recycle CO₂ stream of the NET Power System is also heated using heat derived from the compression energy of the air feed of the O₂ production plant. All fuel and combustion derived impurities such as sulfur compounds, NO, NO₂, CO₂, H₂O, Hg and the like are separated for disposal with no emissions to the atmosphere.

The systems and methods of the present disclosure specifically can be characterized as being a combination of a POX system and power production system (PPS). The NET Power system is an example of a PPS that can be used according to the present disclosure. In particular, a POX fuel gas stream can be introduced to the PPS combustor as part or all of the fuel stream for the combustor. In a high pressure combustion cycle, the fuel gas from the POX stream must in general be compressed to the high pressure required in the power production system combustor. For example, the POX fuel gas stream may be compressed in a compressor to a pressure of at about 10 MPa or greater, about 15 MPa or greater, about 20 MPa or greater, or about 25 MPa or greater. In other embodiments, the pressure can be about 8 MPa to about 50 MPa, about 15 MPa to about 45 MPa, or about 20 MPa to about 40 MPa.

The POX fuel gas stream arising from the reaction of the oxygen with a solid or liquid fuel can comprise varying amounts of solids and molten solids that must be removed before introduction of the POX fuel gas stream into the PPS combustor. Specifically, the POX fuel gas stream can be quenched and cooled as necessary to a temperature wherein ash and other solid materials can be removed. This is beneficial to prevent downstream contamination of equipment in the POX system and the PPS. The heat liberated during cooling of the POX fuel gas stream can be transferred to the power production system to maximize overall efficiency of the power production system. In particular, this heat can be used for partially heating at least a portion of the recycle CO₂ fluid circulating in the power production after cooling of the combustion product stream and prior to input of the recycle CO₂ fluid back into the combustor of the power production system. In particular, the heat can be added to the recycle CO₂ fluid following the compression of the recycle CO₂ fluid. Optionally the oxygen required for the POX reactor and/or the power production system combustor can also be heated against the cooling POX stream in the same or a different heat exchanger.

The POX reactor can be adapted to provide an output POX fuel gas stream having a temperature that is about 1200° C. or greater, about 1300° C. or greater, or about 1400° C. or greater. More particularly, the temperature can be about 1000° C. to about 2000° C., about 1200° C. to about 1800° C., or about 1300° C. to about 1600° C. In various embodiments, one or more steps can be utilized to cool the POX stream (and thus the fuel gas for input to a further combustor), preferably to about ambient temperature.

In one step, the POX stream immediately exiting the POX reactor at a temperature as described above can be quenched to a lesser temperature. Quenching reduces the temperature preferably to 400° C. or less which is a region where the velocity of the BOUDOUARD reaction is so low that no carbon formation or metal dusting corrosion will occur. Quenching to a temperature of 400° C. or less serves to condense volatile metal salts for subsequent removal. The quenching step can be adapted to reduce the temperature of the POX stream to a lesser temperature that can be defined by a ratio in relation to the POX reaction temperature. In particular embodiments, the ratio of the POX reaction temperature to the temperature of the quenched POX stream can be about 3.25:1 or greater, about 3.5:1 or greater, or about 4:1 or greater. More particularly, the temperature ratio of the POX stream to the quenched POX stream can be about 3.25:1 to about 6:1, about 3.75:1 to about 5.5:1, or about 4:1 to about 5:1. In particular embodiments, the temperature of the quenched POX stream can be about 400° C. or less, about 350° C. or less, or about 300° C. or less. In particular embodiments, the temperature can be about 200° C. to about 400° C., about 225° C. to about 375° C., or about 250° C. to about 350° C. Quenching can be carried out by mixing of the POX stream with one or more quenching fluids. Non-limiting examples of quenching fluids that can be used according to the present disclosure include a stream of recycled POX product (i.e., at least a portion of the POX product that has been already cooled to a quenching fluid temperature then cooled in the POX gas heat exchanger followed by liquid water separation), water at a quenching fluid temperature, liquid CO₂, mixtures thereof, and the like. A useful quenching fluid temperature can be about 150° C. or less, about 100° C. or less, about 75° C. or less, or about 60° C. or less. The quenching fluid temperature particularly can be about 10° C. to about 150° C., about 15° C. to about 100° C., or about 20° C. to about 75° C. Alternately the quenching fluid can be preheated against the cooling quenched POX gas or by other means to a temperature approach of typically about 20° C. below the POX quench temperature. In embodiments using a water quench, a portion of the water can be vaporized thus giving a mixture of fuel gas, steam, and a liquid water portion, which washes out the bulk of the ash particles. The temperature of the total liquid and vapor will be determined by the pressure used in the POX reactor and the quantity of liquid water used for the quench.

A further step can provide for separation of any liquid water and the bulk of any ash particles or further solids from the quenched POX stream vapor. Removal of the solids can be carried out using any conventional separation or filter means. Non-limiting examples of suitable solids removal components include cyclone filters, settling tanks, candle filters, bag filters, liquid wash towers, and the like. In some embodiments, a separator can be provided in the lower part of the POX reactor. The separated vapor in general can be introduced into the base of a counter current water wash column to remove further traces of particulate ash. The cleaned POX fuel gas plus steam stream can then optionally be passed through a gas filter, such as a candle filter, to ensure that there can be no deposition of particles in the heat exchanger used for cooling the fuel gas or in the downstream PPS. In some embodiments, a liquid CO₂ stream can be used as the quench fluid. In this case the total stream after quench may consist of a single vapor phase with entrained solid particles. The quantity of liquid CO₂ used for quench can be such that the temperature of the quenched stream is about 200° C. to about 400° C. The ash can be removed in a series of filters as noted above. In other embodiments, a cooled separated fuel gas stream following water separation can be used as part or all of the quench fluid. In various embodiments, a preferred method of quench may use water. The system may also use a mixture of water and CO₂ in which the quantity of water is sufficient to produce enough liquid water following quench to wash out the bulk of the ash particles.

In yet another step, the quenched POX stream (preferably after filtering of solids) can be cooled to near ambient temperature. Accordingly, the disclosed systems and methods can include one or more components adapted for heat exchange. In particular, a heat exchanger can be adapted to transfer the heat from the quenched POX stream to one or more portions of the high pressure CO₂ recycle stream utilized in the power production system. For example, the heat can be transferred to the high pressure CO₂ recycle stream taken from the CO₂ recycle compressor discharge and/or to one or more appropriate points in the recuperator heat exchanger that is used in the power production cycle. The choice of temperatures for the injection of heat to the PPS recuperator heat exchanger and the number and inlet temperature of the streams taken from the PPS recuperator heat exchanger to be heated in the quenched fuel gas cooler can be determined by altering the heat recovery process to ensure heat recovery is at the maximum temperature level consistent with economic heat exchanger sizes.

The solid fuel used in the POX reactor can be provided in a variety of forms. In embodiments noted above, a solid fuel can be provided in a particulate form, preferably a finely powdered state and can be slurried with a slurry medium. In preferred embodiments, the slurry medium can comprise, for example, water, liquid CO₂, and combinations thereof. Liquid CO₂ can be formed, at least in part, from recycled CO₂ from the power production system. The use of CO₂ as the slurrying fluid can be particularly useful to reduce the heat required to raise the temperature of the POX fuel feed to the POX reactor range as compared to the use of a different slurry medium such as water (e.g., water condensed and separated from the power production system). Although CO₂ can be a preferred slurrying medium, other materials, including water, may still be used as desired and may lead to acceptable losses in efficiency under certain embodiments of the present disclosure. The carbonaceous fuel used in the POX reactor can be a liquid such as heated bitumen, in which case no slurrying fluid may be needed.

When using CO₂ or water as the slurrying medium, the composition of the POX stream leaving the POX reactor can have a high carbon monoxide (CO) concentration and partial pressure. In such embodiments, it can be particularly desirable to ensure that quenching of the POX stream is adapted to cool the stream and thus form a quenched POX stream having a temperature of less than 400° C. Providing such temperature drop can particularly limit BOUDOUARD reaction kinetics to a sufficiently low state such that no carbon can be deposited in the POX stream heat exchanger and such that no metal dusting corrosion can take place in downstream equipment.

In relation to particular embodiments, the systems and methods of the disclosure can encompass at least the following four sets of operating conditions in relation to the combination of the POX fuel feed and the POX heat exchange: CO₂ fuel slurry with CO₂ quench; CO₂ fuel slurry with water quench; water fuel slurry with water quench; and water fuel slurry with CO₂ quench. It is understood, however, that other combinations may arise based upon utilization of further slurrying media and/or further quenching fluids. Moreover, the fuel slurry medium can be a combination of water and CO₂. Likewise, the quenching fluid can be a combination of water and the cooled POX stream.

Heat liberated by cooling the quenched POX stream in the heat exchanger following ash removal can be transferred to one or more portions of the high pressure CO₂ recycle stream taken from the power production system. The quench fluid can be recycled POX fuel gas leaving the cool end of the POX heat exchanger following liquid water separation, or it can be condensed and separated water. It also can be a combination of fuel gas and water. Still further, it can be recycled CO₂, or a combination of fuel gas, or water, or both with CO₂. In some embodiments, the source of the quench fluid can be particularly relevant. Embodiments utilizing a CO₂ slurrying medium can result in a net production of water derived from hydrogen and water present in the solid fuel feed (e.g., coal). Separated liquid water thus can be treated to separate flammable components dissolved in the water. These separated flammables can be compressed and returned to the power production system combustor. The cleaned water stream then can be recycled to either the solid fuel slurrying system or the POX quench system, and any surplus water can be sent to the power production system where it can be used to dilute any H₂SO₄/HNO₃ acid produced at the water separation stage in the power production system as described in U.S. Patent Application Publication No. 2011/0179799. In embodiments wherein the solid fuel is slurried with water, the water present in the high temperature POX stream can react with the CO produced by partial oxidation of the carbon in the solid fuel to produce hydrogen gas and carbon monoxide. These can be present in a ratio of approximately 1:1 H₂ and CO by volume.

This consumption of water in the shift reaction can be indicative of a water deficiency, and water produced in the power production system then can be returned to the POX system to produce the solid fuel coal slurry and thus make up for this consumption. The net, cooled POX stream (i.e., the fuel gas stream) then can be compressed to the required pressure for combustion in the power production combustor. In various embodiments, the system and method of the present disclosure can be adapted for production of an internal quench fluid for use with the high temperature POX stream exiting the POX reactor. This can arise from the sequential steps of POX reaction, solids removal, heat exchange cooling, and water separation. The net quantity of fuel gas from the POX stream can be compressed and delivered to the power production system combustor with a relatively high concentration of flammable gases (e.g., H₂ and CO) and with a calorific value which will ensure useful combustion conditions in the power production system combustor.

In some embodiments, a POX reactor according to the disclosure can be adapted to operate at a pressure that is higher than the pressure in the power production system combustor. The power production system combustor particularly can use CO₂ as the working fluid that is continuously recycled in the system. Preferably, the POX stream can be quenched and cooled via heat exchange as described herein using either cooled POX stream or water as the quench medium, and the cooled POX stream (i.e., a fuel gas) can be used in the power production system without the need for further compression. The POX reactor can comprise any reactor adapted for combustion of a carbonaceous fuel, particularly wherein the fuel is only partially oxidized, and particularly wherein the reactor is adapted to function at a pressure that is greater than the operating pressure of a power production system combustor as described herein. In exemplary, non-limiting embodiments, a POX combustor can utilize transpiration cooling wherein a cooling fluid, such as CO₂, is passed through a porous transpiration layer surrounding the POX combustion chamber, which can be particularly useful to prevent ash impingement and agglomeration. Exemplary embodiments of transpiration cooling that can be used with a POX reactor according to the present disclosure are described in U.S. Patent Application Publication No. 2010/0300063 to Palmer et al., U.S. Patent Application Publication No. 2011/0083435 to Palmer et al. and U.S. Patent Application Publication No. 2012/0073261 to Palmer et al., the disclosures of which are incorporated herein by reference in their entireties.

In further embodiments, a POX reactor according to the disclosure can be adapted to operate at a pressure that is below the pressure of the power production system combustor. In such embodiments, a POX stream for use as a fuel in the power production system combustor can be compressed before passage into the power production system combustor. The POX reactor can comprise any commercially available system. Non-limiting examples of commercially available systems useful according to the present disclosure include a Shell dry powdered coal feed entrained flow reactor, a GE/Texaco quench reactor, a Siemens cooling screen quench reactor, or similar systems. Useful POX reactors can include internal heat transfer sections absorbing radiant heat from the POX burner. In such embodiments, a portion of the high pressure recycled CO₂ stream from the power production system can be heated and returned at a higher temperature to the PPS system. For example, recycled CO₂ at a temperature of about 400° C. or higher can be heated to a temperature of about 450° C. to about 600° C. within the POX reactor and returned to the recuperative heat exchanger in the power production system where it can be remixed with a further portion of the high pressure recycle CO₂ stream at a similar temperature.

Combination of a POX reactor with a power production system according to the present disclosure can provide a variety of useful aspects. As an example, the combination can be defined in that impurities (such as from coal or other solid fuel and from partial oxidation of the fuel) can be retained in the cooled, high pressure POX stream that enters the power production system combustor. Such impurities can comprise H₂S, COS, CS₂, HCN, NH₃, Hg. These and other impurities can be oxidized in the power production system combustor so as to form, for example, SO₂, CO₂, N₂, NO, and Hg, which then can be removed from the power production system. For instance, a water stream condensed from the power production system combustor exit stream can be acidic comprising one or more of HNO₃, H₂SO₄, and dissolved inorganic salts, such as described in U.S. Patent Application Publication No. 2011/0179799.

The processing of the solid fuel through the POX reactor rather than directly through a power production system combustor can be particularly useful in light of the ability to remove possibly fouling reaction products. For example, a POX stream exiting the POX reactor can be quenched to a temperature of about 400° C. or less or a further temperature useful to ensure that ash derived from coal (or other molten impurities arising from coal or other solid fuel) is in a solid form which can be removed. Preferably, solid impurities can be removed down to a very low concentration and sufficiently low particle size so as to substantially prevent blockage and/or corrosion of components of the power production system, such as heat exchangers, turbines, compressors, and the like.

In addition to the foregoing, the quenching of the POX stream from the POX reactor can be adapted to provide a quenched POX stream below a temperature as defined herein and is sufficiently low to ensure that the vapor phase concentration of any inorganic components in the solid fuel is likewise sufficiently low to substantially prevent deposition in one or more components of the power production system. For example, partial oxidation of coal can produce one or more alkali metal salts including NaCl, CaSO₄, and KCl, which can be removed as discussed herein. The upper temperature limit of the quenched POX stream also can be adapted to ensure that the BOUDOUARD reaction is sufficiently slow so as to substantially prevent carbon deposition and/or metal dusting corrosion in any heat exchanger or other components in the power production system.

The systems and methods of the present disclosure can be adapted to provide for recovery of substantially all of the heat released during cooling of the POX stream, preferably cooling to near ambient temperature, and recovery of the heat into the recycled high pressure CO₂ stream in the power production system. This additional heating particularly can be provided at the lower temperature level in the recuperator heat exchanger of the power production system. Input of additional heat in this manner can provide a significant positive effect on the overall efficiency of the power production system. This effect is due to the much higher specific heat of the high pressure recycle CO₂ stream in the lower temperature range of 50° C. to 400° C. compared to the higher temperature range of 400° C. to 800° C. and to the lower specific heat of the turbine exhaust stream that is cooling in the recuperator heat exchanger of the power production system. This marked difference means that significant additional extra heat is required in the recuperator heat exchanger over the temperature range 50° C. to 400° C. to heat the recycle CO₂ stream. The additional heat obtained from the quenched POX stream in the POX stream heat exchanger provides an effective quantity of additional heat for the power production system combustor that is substantially equivalent to the quantity of heat released when fuel gas itself is combusted.

In various embodiments wherein the POX reactor is quenched to saturation using a recycle water stream, the temperature-heat release curve for the quenched POX stream cooling to near ambient temperature shows a large initial heat release as the water vapor derived from vaporization of the quench water begins to condense. This heat release per unit temperature drop reduces progressively as the POX stream cools. The effect requires two separate high pressure recycle CO₂ streams taken from the power production system high pressure recycle stream to be used to recover heat from the cooling quenched POX stream. In some embodiments, the first high pressure recycle CO₂ stream can be taken from the CO₂ recycle compressor discharge at the temperature of about 45° C. to about 70° C. The second high pressure recycle CO₂ stream can be taken from the high pressure recycle stream at a point in the recuperator heat exchanger where there is a small temperature approach to the dew-point of the turbine exhaust cooling stream. These two streams together can provide for a large initial heat release from the cooling quenched POX stream as its water content begins to condense that can be efficiently transferred back to the high pressure CO₂ recycle stream at the highest possible temperature level (see FIG. 3). In embodiments wherein the POX stream is initially quenched to about 400° C., a cooling range between about 400° C. and the water dew point of the quenched POX stream exists, and this range can require a lower flow of recycle high pressure CO₂ to efficiently remove this portion of the heat available from the quenched POX stream as compared to the temperature range below the water dew point of the POX stream. This can be accomplished by removing a portion of the heating high pressure recycle CO₂ stream at a point near and/or below the water dew-point temperature of the quenched POX stream while the remaining portion is removed at a temperature near to and/or below the quench temperature (e.g., about 400° C.) (see FIG. 4). The heated high pressure recycle CO₂ streams then can be returned to the recuperator heat exchanger at a corresponding temperature point to the bulk flow of high pressure recycle CO₂ in the recuperator heat exchanger. In various embodiments, options for the two streams to combine in the POX cooling heat exchanger with a single return stream can be provided. In some embodiments, more than two streams of high pressure recycle fluid can be used.

In some embodiments, the fuel gas taken from the POX reactor following quench and ash removal can comprise predominantly H₂, CO, CO₂ and H₂O at a temperature of about 250° C. to about 400° C. A portion of this fuel gas stream can be taken for the production of pure H₂, CO, or a combination thereof with varying H₂ to CO ratios. Typical applications for large scale H₂ production can be, for example, hydro-desulfurization and hydrocracking in refineries and, potentially, as a vehicle fuel. Typical applications for H₂ and CO mixtures can be, for example, Fischer-Tropsch hydrocarbon liquids production (e.g., with about a 2.2H₂ to CO ratio) and methanol production (e.g., with about a 2.0H₂ to CO ratio). In each case, the H₂ to CO ratio must be increased from the ratio of approximately 1 or less in the POX fuel gas stream where the ratio depends on use of CO₂ or water as the slurrying medium for the solid fuel. Water based slurry with more water in the POX product gas results in a significant proportion of the CO being converted to H₂ and CO₂, giving a H₂ to CO ratio of just below 1. CO₂ based slurry has a much lower H₂ to CO ratio. It can be useful to pass at least part of the separated quenched POX fuel gas stream through a catalytic shift reactor to convert CO to H₂ by reaction with steam, as shown below in Formula (2).
CO+H₂O=H₂+CO₂  (2)
This can be accomplished using a portion of the fuel gas taken at a temperature of about 250° C. to about 400° C. following ash removal and by using a sulfur tolerant CO shift catalyst, such as one based on cobalt in the shift reactor. The portion of fuel gas that has been enriched in H₂ can be then cooled in a separate pass through the POX heat exchanger. Heat released in the exothermic shift reaction can be transferred into the PPS as previously described. The exit shifted gas then can be mixed with a portion of the remaining cooled POX stream and the combined stream can be passed through a multi-bed pressure swing adsorber designed to separate the H₂ and CO at the required H₂ to CO ratio as a single non adsorbed component while the adsorbed components can contain all of the sulfur compounds, HCN, NH₃, Hg, CO₂, H₂O and most of the CH₄. This un-adsorbed fraction may also contain some N₂ and Ar derived from the coal (or other solid or liquid fuel) and oxygen used in the POX reactor. These inert components preferably will be below 5% total concentration which is acceptable for the gas feed to both the Fischer-Tropsch and Methanol reactors. If pure H₂ production is required, only the shifted cooled gas will be fed to the PSA. The near atmospheric pressure waste gas from the PSA with all of the coal and POX derived impurities in a reduced form will be compressed and returned to the remaining POX fuel gas for combustion in the PPS combustor.

One embodiment of a power production system with partial oxidation of a solid fuel is described in reference to FIG. 1, wherein a solid fuel is provided in the form of coal feed stream 21 to be partially oxidized in the POX reactor 4. The coal stream 21 is crushed and partially dried in large particle crusher 1 that is also fed dry nitrogen stream 23 comprising N₂ at a temperature of about 82° C. (180° F.) taken from an air separation unit 6, which produces oxygen streams 32 and 60 and nitrogen stream 23 from air intake stream 62. Preferably, the dry nitrogen stream 23 can be heated against a higher temperature stream of CO₂ rich turbine exhaust leaving the recuperator heat exchanger in the PPS. The coal is further crushed to a particle size preferably of about 250 microns or less in the small particle crusher 2 to provide particularized coal stream 25, which is directed to a slurry mixer 3. In the slurry mixer 3, the particularized coal is mixed with CO₂ slurry medium stream 29, which preferably has a pressure of about 8.5 MPa or greater. The CO₂ in the CO₂ slurry medium stream 29 in this embodiment is at a temperature of about 17° C. The CO₂ in the CO₂ slurry medium stream 29 has a density of about 865 kg/m³. The powdered coal is increased in pressure in a lock hopper system or by other means to a pressure of 8.5 MPa prior to mixing with the CO₂. A coal/CO₂ slurry stream 26 exits the slurry mixer 3 and preferably comprises about 45% by weight coal. Alternatively the slurry medium can be a water stream. The powdered coal injection system can also be configured as a dry feed system in which the powdered pressurized coal is entrained in a nitrogen stream and fed into the POX burner. The slurry stream 26 is then pumped into the POX reactor 4 where it is combined with oxygen stream 56, which preferably comprises 97% molar or greater oxygen concentration. The POX reactor 4 preferably operates at a pressure of about 8.5 MPa and a temperature of about 1400° C.; however, the temperature and pressure can be in any combinations of temperature and pressure ranges as otherwise disclosed herein in relation to the nature of the POX stream exiting the POX reactor. The conditions for the preparation of the coal slurry can be adjusted accordingly.

The POX reactor 4 is adapted to partially oxidize the coal and form a POX stream, which may exit the POX reactor and enter a quench chamber (not illustrated) or may be quenched within the POX reactor itself, as illustrated in FIG. 1. The POX stream can comprise a fuel gas that can comprise one or more combustible (i.e., oxidizable) materials, including but not limited to H₂, CO, CH₄, H₂S, COS, CS₂, HCN, NH₃. Moreover, the POX stream can comprise Hg and other impurities derived from the coal (or other solid fuel) as well as inert materials (e.g., N₂ and Ar), such as derived from the oxygen stream 56, plus other trace components. The POX stream also can comprise one or more non-combustible materials, such as ash or slag, which can be filtered from the POX stream as desired.

The POX stream (either internal to the POX reactor or in a separate component) is quenched by mixing with a quench fluid (liquid water stream 57 in the present embodiment). As illustrated, the liquid water stream 57 enters the POX reactor near the base in a restriction nozzle. The addition of the quench stream cools the POX stream components preferably to below the water saturation temperature of about 304° C. (although higher temperatures also are encompassed). The quench temperature preferably also can be a temperature at which non-combustibles, such as ash and slag, are in solid form. The excess quench water collects with the slag and the bulk of the fine ash in the sump of the POX reactor vessel (or separate quench vessel) where it is removed for further treatment. The quenched POX stream 58 passes to scrubber unit 5, which comprises a water scrub tower followed by a fine cartridge filter adapted to reduce the dust load to about 4 mg/m³ or less of fuel gas, about 3 mg/m³ or less of fuel gas, or about 2 mg/m³ or less of fuel gas. Scrubber unit 5 also can include all equipment and pumps required to recycle the scrub water and also to treat the ash stream 66 for disposal. An exemplary embodiment of a system useful for POX reactor ash treatment and gas cleaning is a GE/Texaco POX system with a coal/water slurry burner, which alternatively can be modified to accept a coal/CO₂ slurry.

The cleaned fuel gas plus steam stream 55 is cooled in heat exchanger 7. The exit stream 59 is further cooled against cooling water in heat exchanger 9. Liquid water 46 is separated in separation vessel 8 from the inlet stream 61 and pumped in pump 11 back to the POX reactor quench and some addition makeup water from stream 38 to produce quench water stream 57. The net fuel gas stream 47 is compressed in a multi-stage centrifugal compressor 10 to a pressure suitable for input as stream 48 to the power production system combustor 14. As an example, the fuel gas stream 47 can be compressed to a pressure of about 30.5 MPa. The compressed fuel gas stream 48 is heated in the recuperator heat exchanger 12 to a temperature suitable for input to the power production system combustor 14. As an example, the compressed fuel gas stream 48 can be heated to a temperature of about 746° C. The heated fuel gas stream 64 is burned in the power production system combustor 14 where it is combined with oxygen and CO₂. In the illustrated embodiment, combined O₂/CO₂ stream 51 comprises 30% O₂ and 70% CO₂ on a molar basis. The combined O₂/CO₂ stream 51 preferably been heated to a temperature suitable for input to the power production system combustor 14. As an example, the combined O₂/CO₂ stream 51 can be heated to a temperature of about 746° C. in the recuperator heat exchanger 12. A hot recycle CO₂ stream 52 is directed from the recuperator heat exchanger 12 and is at a temperature suitable for input to the power production system combustor 14. As an example, the hot recycle CO₂ stream 52 can be heated to a temperature of about 746° C.

In the power production system combustor, the combustion gases from burning of the fuel gas are cooled with the hot recycle CO₂ stream 52 producing a combined combustion product stream 50 at a temperature of about 1150° C. and a pressure of about 30 MPa in the illustrated embodiment. This is expanded to a pressure of about 3 MPa in turbine 13 coupled to an electric generator 65 producing an output power 63. The turbine outlet stream 49 is cooled in the recuperator heat exchanger 12 leaving as cooled product stream 53 at a temperature of about 64° C. in the illustrated embodiment. The stream 53 is cooled to a temperature of about 17° C. in water cooler 16. The further cooled turbine outlet stream 54 enters a scrub tower 17, which has an outlet stream 40 that is largely recycled via circulation pump 18 to scrub tower liquid inlet 41 above the packed section of the tower that receives the further cooled turbine outlet stream 54. A portion of stream 40 is split out as stream 39 for further treatment. As the turbine exhaust gas cools below the water dew-point in the recuperator heat exchanger 12 the following reactions occur.
NO+½O₂═NO  (3)
NO₂+SO₂=SO₃+NO  (4)
SO₃+H₂O═H₂SO₄  (5)

The above reactions will proceed in the presence of liquid water, nitrogen oxides, SO₂/SO₃, and excess oxygen. The SO₂/SO₃ concentrations are reduced to very low levels since the limiting reaction shown in Formula (3) rapidly proceeds at 3 MPa, and the reactions of Formula (4) and Formula (5) are very fast. When all of the sulfur oxides have been converted to sulfuric acid, the nitrogen oxides are converted at about 95% conversion rate per pass to nitric acid with the following reaction sequence.
2NO₂+H₂O=HNO₂+HNO₃  (6)
3HNO₂=HNO₃+2NO+H₂O  (7)
NO+½O₂═NO₂  (8)

Returning to FIG. 1, the nitric acid present in net liquid acid product stream 39 will convert any mercury present to mercuric-chloride. The scrub tower 17 preferably is fitted with an additional water wash and acid mist removal section. Its primary function is to act as an efficient dilute acid removal device since virtually all the above reactions will have taken place upstream of the scrub tower 17. The mixed acids are treated with limestone slurry stream 36 (or other suitable base) in mixer 15 to produce gypsum and calcium nitrate stream 37. Any other trace metallic salts can also be separated. The residual water stream 38 following calcium nitrate and dissolved salts removal can be used as make-up to a cooling tower or the POX quench system or as scrub water recycled to scrub tower 17.

The predominantly CO₂ stream 42 leaving the scrub tower 17 at a pressure of about 2.9 MPa is compressed in a multi-stage intercooled compressor 19 followed by a dense fluid multistage pump to a pressure suitable for input to the power production system combustor, such as about 30.5 MPa. The compressed CO₂ discharge stream 35 leaves the last stage of the pump 19 at a temperature of about 54° C., and part of this flow, stream 70, is heated in the recuperator heat exchanger 12 to a temperature of about 746° C., leaving as CO₂ stream 52.

The air separation plant 6 in this embodiment produces a 99.5% molar oxygen purity product stream at a pressure of about 8.6 MPa which divides into two separate streams. Oxygen stream 60 is heated in heat exchanger 7 to a temperature of about 294° C., exiting as stream 56 for use in the POX reactor 4 for partial oxidation of the coal. The remaining oxygen stream 32 is mixed with CO₂ at a pressure of about 8.6 MPa. Specifically, CO₂ is taken from an intermediate stage of the compressor 19 as stream 30, and a portion stream 31 mixes with oxygen stream 32 giving a composition of about 30% O₂ and 70% CO₂ molar. This diluted O₂ stream 33 is compressed to a pressure of about 30.5 MPa in a multi-stage intercooled compressor 20 and the discharge stream 34 is heated in the recuperator heat exchanger 12 to a temperature of about 746° C. and enters the power production system combustor 14 as stream 51. Dilution of the pure O₂ stream 32 is beneficial to allow the oxygen required for combustion in the power production system combustor 14 to be heated to a high temperature without the need for oxidation resistant materials. This ensures the safe operation of the power production system. The 30% O₂ stream is useful to moderate the adiabatic combustion temperature in power production system 14 to a value of approximately 2400° C. The remaining portion of CO₂ stream 30 is CO₂ stream 29, which provides the CO₂ for slurrying the powdered coal and is directed to slurry mixer 3.

Cooling of the quenched POX gas in heat exchanger 7 is useful to transfer the maximum quantity of heat to the power production system to maximize the overall efficiency. The power production system requires a significant quantity of heat from an external source in the temperature range from near ambient up to about 400° C. This can be provided by using adiabatic air compressors in the air separation plant 6 and transferring the heat of compression to part of the high pressure recycle CO₂ stream. In the present embodiment, the required external heating load is provided by cooling the quenched POX gas in heat exchanger 7 and heating two high pressure recycle streams. High pressure recycle CO₂ stream 28 at a temperature of about 54° C. and high pressure recycle CO₂ stream 43 at a temperature of about 120° C. taken from an intermediate temperature point in recuperator heat exchanger 12 are heated to provide a combined heating outlet stream 44 at a temperature of about 294° C., which is returned to mix with the main recycle CO₂ stream at a corresponding temperature point in recuperator heat exchanger 12. Optionally, outlet stream 67 also may be returned to the recuperator heat exchanger at a corresponding temperature point to mix with the main recycle CO₂ stream as well.

Illustrated in FIG. 3 is a plot of temperature against percentage heat release (diagrammatically) in the recuperator heat exchanger 7 of FIG. 1 to show the benefit of two separate inlet streams of high pressure recycle CO₂ to ensure efficient operation of the combined system. The 120° C. temperature level of stream 43 inlet corresponds to a temperature approach to the water dew-point of the turbine exhaust stream in recuperator heat exchanger 12. The quenched POX fuel gas enters the heat exchanger at the water saturation temperature of 304° C., and the total heated high pressure recycle stream leaves at a temperature of 294° C.

Shown in FIG. 4 is an alternative method of operation in which the quench water stream reduces the POX gas temperature to about 400° C. There is an additional section of heat exchanger in which the quenched POX fuel gas temperature falls to its dew-point of about 300° C. To maximize the efficiency of the total power production system by minimizing the temperature difference in heat exchanger 7, the high pressure heated CO₂ stream is removed from the heat exchanger as two separate streams. Stream 44 is at a temperature of about 290° C. and stream 67 is at a temperature of about 390° C. These streams are separately returned to recuperator heat exchanger 12 where they reunite with the main high pressure recycle CO₂ stream at the appropriate corresponding temperatures.

In exemplary embodiments, heat exchanger 7 can be a high pressure brazed or diffusion bonded multi-channel unit. The material of construction preferably is corrosion resistant in the presence of the impurities present in the POX gas plus liquid water. Recuperator heat exchanger 12 preferably is a diffusion bonded multi-channel unit. This unit preferably is adapted for operation at temperatures up to about 800° C. and to be resistant to acid corrosion at temperatures below about 200° C. An exemplary suitable material is Specialty Metals alloy 740. In some embodiments, the average temperature at the hot end of heat exchanger 12 can be reduced to below 750° C. and, in such cases, alloy 617 can be suitable. Optionally the intermediate section between 200° C. and 540° C. can be fabricated from stainless steel. The section which is subject to potential acid corrosion below 200° C. can be constructed to allow replacement at intervals.

In further embodiments, alternate arrangements of the elements for processing the POX stream can be used. In an exemplary embodiment, FIG. 2 shows an optional arrangement wherein the POX product is used both for production of fuel gas for the power production system and for production of a separated and purified mixture of H₂ and CO. A side-stream 66 is taken from the quenched POX gas stream 55 following ash removal and passed through a catalytic shift converter 67 having a sulfur resistant cobalt based shift catalyst (or other suitable material). The higher temperature exit gas stream 70 is cooled in heat exchanger 7 to a temperature of about 60° C., exits as stream 73, and is further cooled by cooling water in heat exchanger 74 to a temperature of about 20° C. as stream 75. Condensed water is separated in separator 77, and the cooled gas stream 76 enters a multi-bed pressure swing adsorption unit 79. The water separated in separator 77 is added to liquid water stream 46. The pressure swing adsorption unit (PSA) 79 is designed to separate the inlet gas stream 76 into a pure H₂ or a pure H₂ and CO stream 80 leaving the unit at a pressure of about 8 MPa and a waste gas stream 71 which contains all of the impurities (e.g., H₂S, COS, CS₂, HCN, NH₃, Hg, and other trace components) as well as some combination of H₂, CO, CO₂, CH₄, and H₂O. The separation of the impurities is such that the concentration of these components in the H₂ or H₂ and CO product stream 80 is below 1 ppm. This arrangement uses a stream 83 of cooled POX gas containing a high concentration of CO to blend with the shifted cooled gas stream 76 to produce a stream 72 which when passed through the PSA unit 79 and gives the required flow and the required H₂ to CO ratio in the 8 MPa product stream 80. If pure H₂ is required then stream 83 is zero. The waste gas stream 71 from the PSA 79 at 0.12 MPa pressure is compressed in a multi-stage intercooled compressor 81 to a pressure of about 8 MPa, and the discharge stream 82 is added to the power production system fuel gas stream 47. The total fuel gas stream is compressed to a pressure of about 30.5 MPa in compressor 10, and the resultant high pressure fuel gas stream 48 is sent to the power production system combustor 14 via recuperator heat exchanger 12 (referencing FIG. 1). This arrangement ensures the transfer of all coal and POX derived impurities to the power production system where they are oxidized in the power production system combustor 14. In various embodiments, the consumption of additional water in the shift reaction can proceed according to Formula (9) and may require a small additional make-up flow.
H₂O+CO=CO₂+H₂  (9)

In various embodiments incorporating elements of the systems and methods described herein, the overall efficiency of the disclosed systems and methods is greater than 50% (on a lower heating value (LHV) basis with representative turbine and compressor efficiencies and heat exchanger temperature differences and pressure drops). Moreover, CCS is simultaneously provided along with substantially complete removal of all other fuel, POX, and combustion derived impurities. Excess CO₂ derived from the carbon in the fuel stream 21 is removed from the circulating CO₂ system as stream 71 at 30.5 MPa. This can be facilitated in that the systems and methods can be adapted to provide substantially all of the fuel derived CO₂ at a pressure of about 15 MPa or greater, about 20 MPa or greater, about 25 MPa or greater, or about 30 MPa or greater. This high efficiency beneficially can be achieved with a low cost system, such as using commercially available POX reactor systems and a high pressure CO₂ working fluid power cycle, such as described in U.S. Patent Application Publication No. 2011/0179799, which is incorporated herein by reference in its entirety. As a comparative example, existing commercial coal based integrated gasification combined cycle (IGCC) power generation systems with CO₂ capture and compression to pipeline pressure have been shown to have efficiencies on a comparable basis of only 34% to 39% and have much higher capital cost.

EXPERIMENTAL

The above described advantages of the presently disclosed methods and systems were verified via extensive ASPEN simulations under a variety of conditions with realistic estimates for commercial equipment performance. Two sets of simulations were carried out using Illinois #6 coal as the solid fuel introduced to the POX combustor. In each case, data is based upon the use of CO₂ as the coal slurry medium. The simulations differed in that the first simulation (see FIG. 5) was based upon the use water as the quenching fluid, and the second simulation (see FIG. 6) was based upon the use of CO₂ as the quench fluid.

Details of the mass and heat balance from the first simulation are provided in the Table shown in FIG. 5. Under the shown conditions, a fuel gas was produced typically with a H₂ to CO ratio of 0.41 to 1. The calculated efficiency for this embodiment on a lower heating value (LHV) basis was 51.44%.

Details of the mass and heat balance from the second simulation are provided in the Table shown in FIG. 6. Under the shown conditions, a fuel gas was produced typically with a H₂ to CO ratio of 0.17 to 1. In each case, hydrogen ratios can be increased with embodiments using water shift. The calculated efficiency for this embodiment on a LHV basis was 51.43%.

Many modifications and other embodiments of the presently disclosed subject matter will come to mind to one skilled in the art to which this subject matter pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the present disclosure is not to be limited to the specific embodiments described herein and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

1. A process for the production of power using a combination of a partial oxidation (pox) system and a power production system (pps), the process comprising:

combining a solid or liquid carbonaceous fuel and oxygen in a pox reactor under conditions sufficient to partially oxidize the solid or liquid carbonaceous fuel and form a pox stream at a first temperature comprising a fuel gas;

cooling the pox stream to a second temperature that is less than the first temperature and thus form a cooled pox stream;

removing at least a portion of any solids present in the pox stream;

separating at least a portion of any water present in the pox stream;

compressing the pox stream to a pressure suitable for combustion in a pps combustor;

combusting the fuel gas in the pox stream in the pps combustor to form a pps combustion product stream;

expanding the pps combustion product stream across a pps turbine to generate power and form an expanded pps combustion product stream;

passing the expanded pps combustion product stream through a pps recuperator heat exchanger and thereby withdrawing heat from the pps combustion product stream and forming a cooled pps combustion product stream;

removing at least a portion of one or more impurities from the cooled pps combustion product stream to form a recycle CO₂ stream; and

pressurizing the recycle CO₂ stream in a pps compressor to form a compressed recycle CO₂ stream.

2. The process according to claim 1, wherein said cooling the pox stream comprises quenching the pox stream through combination with a quenching fluid.

3. The process according to claim 2, wherein quenching comprises mixing the pox stream with: a recycled portion of the cooled pox stream; a portion of the water separated from the pox stream; a portion of the recycle CO₂ stream from the pps; or a combination thereof.

4. The process according to claim 1, wherein said cooling the pox stream comprises cooling the pox stream in a pox heat exchanger against a cooling stream.

5. The process according to claim 1, wherein the pps turbine has an inlet pressure and an outlet pressure such that a ratio of the pps turbine inlet pressure to the pps turbine outlet pressure is 12 or less.

6. The process according to claim 1, wherein passing the expanded pps combustion product stream through the pps recuperator heat exchanger cools the pps combustion product stream to a temperature below a water dew point of the pps combustion product stream.

7. The process according to claim 1, wherein the fuel gas in the pox stream entering the pps combustor comprises at least one fuel gas component selected from H₂, CO, and CH₄.

8. The process according to claim 1, wherein prior to compressing the pox stream, the process further comprises carrying out at least one conversion reaction whereby the pox stream becomes enriched in at least one fuel gas component.

9. The process according to claim 8, wherein the at least one conversion reaction comprises a conversion between a mixture of CO and H₂O and a separate mixture of H₂ and CO₂.

10. A combined partial oxidation (pox) system and power production system (pps) comprising:

a pox reactor adapted to partially oxidize a liquid or solid carbonaceous fuel in the presence of oxygen to form a pox stream comprising a pox fuel gas;

one or more components adapted to cool the pox stream;

a compressor adapted to compress the pox stream to a pressure suitable for combustion and thus form a compressed pox stream;

a pps combustor adapted to combust pox fuel gas in the compressed pox stream with oxygen in the presence of compressed recycled CO₂ and form a compressed pps combustion product stream;

a turbine adapted to expand the pps combustion product stream to form an expanded pps combustion product stream and generate power in a connected generator;

a pps recuperator heat exchanger adapted to transfer heat from the expanded pps combustion product stream;

a pps compressor adapted to compress recycled CO₂ from the expanded pps combustion product stream and form a compressed recycled CO₂; and

flow components adapted to direct a portion of the compressed recycled CO₂ to the pps recuperator heat exchanger so as to be in a heat exchange relationship with the expanded pps combustion product stream.

11. The combined pox system and pps system according to claim 10, wherein the one or more components adapted to cool the pox stream comprises a quench stream entering the pox reactor.

12. The combined pox system and pps system according to claim 10, wherein the one or more components adapted to cool the pox stream comprises a heat exchanger downstream from the pox reactor and upstream from the compressor adapted to compress the pox stream.

13. The combined pox system and pps system according to claim 10, further comprising a pox scrubber downstream from the pox reactor and upstream from the compressor adapted to compress the pox stream and adapted to separate any solids present in the pox stream.

14. The combined pox system and pps system according to claim 10, further comprising a filtration device adapted to separate solidified ash particle from a single phase quenched pox fuel gas stream.

15. The combined pox system and pps system according to claim 10, further comprising a shift reactor.

16. The combined pox system and pps system according to claim 10, further comprising a separator adapted to separate any liquid water from the pox fuel gas.

17. The combined pox system and pps system according to claim 10, further comprising a pps scrubbing tower adapted to separate one or more of H₂SO₄, HNO₃, and water-dissolved Hg salts from the expanded pps combustion product stream and output a recycle CO₂ stream.

18. The combined pox system and pps system according to claim 10, further comprising flow components adapted to direct a portion of the compressed recycled CO₂ to the one or more components adapted to cool the pox stream.

19. The combined pox system and pps system according to claim 18, further comprising flow components adapted to direct a portion of the compressed recycled CO₂ from the one or more components adapted to cool the pox stream to the pps recuperator heat exchanger.